The new teams are part of a broader government effort to shield the nation from destructive attacks over the Internet that could harm Wall Street or knock out electric power, for instance.

But Alexander warned that budget cuts will undermine the effort to build up these forces even as foreign threats to the nation’s critical computer systems intensify. And he urged Congress to pass legislation to enable the private sector to share computer threat data with the government without fear of being sued.

As he moves into his eighth year as director of the National Security Agency and his third year as head of the fledgling Cyber Command, Alexander told the Senate Armed Services Committee that the strategic-threat picture is worsening. “We’ve seen the attacks on Wall Street over the last six months grow significantly,” he said, noting there were more than 160 disruptive attacks on banks in that period.